The maintenance of the edge of your knife requires a material adapted to the type of steel.
Carbon steel and 12C27 stainless steel reguire a natural stone.
440 stainless steel requires a special carbide head sharpener.
Slide the knife-blade over the sharpener several times, being careful to keep an angle of 20° between the knife and the natural stone
Remember to go right to the point of the knife.
If the results are still not satisfactory, it could be that the blade is too worn.
In this case the knife edge needs reworking with a sharpening stone attached to a grinding wheel.
This is a delicate operation which can upset the fine line of the knife edge within seconds.
It is highly recommended to leave this job to a professional.